A Time Window for Distance Information Processing in the Bats, Noctilio Albiventris and Rhinolophus Rouxi

Abstract

Microchiropteran bats emit echolocation sounds that have structured patterns of frequency changes over time. Classes of frequency pattern have been observed among bat orientation pulses. Bat echolocation sounds generally consist of constant frequency (CF) and frequency modulated (FM) elements alone or in a combination of the two components. For example, in certain species (known as CF/FM bats), the echolocation sounds contain a CF component preceding the FM sweep; in some species the CF component is short (under 12 msec), while in others it is long (over 12 msec). The defined structures of echolocation sounds presumably reflex specific information processing requirements. One generally accepted requirement is that a broadband signal is necessary for accurate perception of target distance by neural measurement of the time interval between the emitted broadband event and a returning echo. Nevertheless, the essential elements and processing requirements of complex CF/FM echolocation sounds has mostly been a matter of conjecture. In this paper I describe experiments that demonstrate which structural elements of complex CF/FM echolocation sounds code target distance information and provide a mechanism regarding hcw this information is processed by the nervous system. These studies suggest that CF/FM bats use both the CF and FM components of their CF/FM echolocation sounds for the determination of target distance, with the onset of the CF component activating a gating mechanism that establishes a time window during which FM component pulse-echo pairs are processed for distance information.